1. Field of the Invention
This invention relates to a video signal reproducing apparatus and more particularly to an apparatus adapted for reproduction of a composite signal formed by superimposing four kinds of pilot signals of different frequencies upon a video signal, one upon each portion of the video signal for a predetermined period in a predetermined sequence of rotation, for recording tracks formed on a recording medium.
2. Description of the Prior Art
For reproduction of a video signal recorded on a video recording tape such as magnetic tape with a rotating head of a video tape recorder (hereinafter called a VTR), tracking methods have been proposed for accurately tracing the recording tracks of the video signal at the reproduction time. Such tracking methods of the prior art include a first method in which a control signal is recorded along an edge of the video tape for tracking control and a second method in which four kinds of pilot signals of different frequencies are recorded beforehand by superimposing them on the video signal. The details of the second method are as follows:
In the accompanying drawings, FIG. 1 shows a recording pattern on a video recording or reproducing tape. The illustration of FIG. 1 includes a video tape 10; an area 11 provided for obtaining a reproduced video signal; overlapped recording areas 12 and 13 on which the video signal is overlappingly recorded; a first recording/reproducing head 14 (hereinafter called A head); and a second recording/reproducing head 15 (hereinafter called B head). The recording/reproducing heads 14 and 15 have azimuth angles which differ from each other. Video signal recording tracks A1-A7 are recorded by the A head 14 while video signal recording tracks B1-B6 are recorded by the B head 15. Pilot signals (hereinafter called signals F1, F2, F3 and F4) of four different frequencies f1, f2, f3 and f4 are recorded in the recording tracks A1-A7, B1-B6, one for every video signal field period, by superimposing them upon the video signal.
A pilot signal reproduced by the reproducing head is multiplied by a reference signal frequency which is substantially the same as that of a pilot signal superimposed on a recording track which is mainly traced (hereinafter called the main track) by the reproducing head. Then, crosstalk components from adjacent tracks located in front of and behind the main track are separated from a multiplication output thus obtained. The levels of these two crosstalk components are compared with each other to obtain a tracking control signal which corresponds to the positional error of the reproducing head relative to the main track.
This method makes it possible to obtain tracking control signals throughout the video signal recording track and thus ensures accurate tracking even for a curved video signal recording track. Furthermore, when the reproducing head is mounted on an electric-to-mechanical converting element such as a bi-morph element, shifting its rotating face in a direction intersecting the video signal track, accurate tracking can also be accomplished even when the tape 10 moves at a speed different from the speed at which recording is performed. In that instance, however, multiplication must be performed by accurately determining the same frequency reference signal as that of the pilot signal recorded in the main track. For example, when reproduction is to be performed on the recorded tape 10 of FIG. 1 at a reproducing speed three times the recording speed, reproduction is performed as follows: After the record of the track A1 (frequency f1) is reproduced by the A head 14, the track B2 (f3) is reproduced by the B head 15. Then, the A head 14 reproduces the track A4 (f4) and the B head 15 the track B5 (f2) and the tracks are thus reproduced one after another. Meanwhile, the reference signal frequency used for multiplication changes for every field such as f1-f3-f4-f2-f1-f3 - - - , which differs from the frequency rotation (f1-f2-f4-f3) of the pilot signals with which recording is accomplished. This can be understood from the following table which shows frequency rotations which take place during reproducing operations carried out at various higher speeds determined by integral numbers times the recording speed:
TABLE 1 ______________________________________ Frequency shifting rotation for reproduction at tape speeds, which are integral numbers, times as, speeds as high as the recording tape 10 speed K Frequency rotation ______________________________________ 4n f1 f2, f2 f4, f4 f3, or f3 f1 4n + 1 f1 .fwdarw. f2 .fwdarw. f4 .fwdarw. f3 .fwdarw. f1 .fwdarw. . . . 4n + 2 f1 f2, f2 f4, f4 f3, or f3 f1 4n + 3 f1 .fwdarw. f3 .fwdarw. f4 .fwdarw. f2 .fwdarw. f1 .fwdarw. f3 .fwdarw. . . ______________________________________ . Notes K: The multiplying rate of the reproducing tape speed relative to the tap 10 speed adopted for recording n: an integer
While the above table shows the frequency rotation for reproducing operations carried out at tape speeds, which are integral numbers times speeds as high as the tape speed used for recording, frequencey rotation becomes more complex for reproduction carried out at tape speeds which increase at multiplying rates other than those obtained by multiplying by the integers.
FIG. 2 is a circuit diagram showing a circuit which effects the rotation of the reference signal frequencies to be generated. FIG. 3 is a timing chart showing the operation timing of the circuit in FIG. 2.
Referring to FIG. 2, a magnetic head 21 detects the position of a video head of a cylinder 20 on which the rotating video head is mounted. The output of the magnetic head 21 is delayed by a monostable multivibrator 22. The output is then changed by a flip-flop (hereinafter called FF for short) 23 into a head switch-over pulse signal SEA (corresponding to the signal 30 PG). The head switch-over pulse signal SEA is then supplied to a data selector 25. Meanwhile another signal SEB is obtained by frequency dividing the head switch-over pulse signal SEA. The signal SEB is also supplied to the data selector 25. The data selector 25 operates as shown in the following table:
TABLE 2 ______________________________________ Truth values of data selector 25 Selected input Data input Reference SEA SEB f1 f4 f2 f3 signal produced ______________________________________ H L H -- -- -- f1 H H -- H -- -- f4 L L -- -- H -- f2 L H -- -- -- H f3 ______________________________________
As shown in Table 2 and FIG. 3, the the reference signal frequency produced changes in synchronization with the timing of the head switch-over and becomes f4 when both the head switch-over pulse signal SEA and the signal SEB are produced at a high leve (hereinafter called H); becomes f3 when the head switch-over pulse signal SEA is at a low level (hereinafter called L) and the signal SEB is at H; becomes f1 when the head switch-over pulse signal SEA is at H and the signal SEB is at L; and becomes f2 when both the head switch-over pulse signal SEA and the signal SEB are at L. However, this arrangement does not enable the apparatus to shift the frequency rotation based on the tape 10 speed set at the time of reproduction. The tape 10 speed at which reproduction can be accomplished is thus limited to speeds 4n+1 times as high as the tape 10 speed used for recording.
It is therefore an object of the present invention to provide a video signal reproducing apparatus which is capable of eliminating the above shortcoming of the apparatus of the prior art.
It is another object of the invention to provide a video signal reproducing apparatus which, despite an extremely simple structural arrangement, is capable of satisfactorily performing tracking control when reproducing at a recording medium moving speed 4n+3 times as high as the speed at which recording is performed.
It is a further object of the invention to provide a video signal reproducing apparatus which permits satisfactory tracking control for reproduction at a recording medium moving speed 4n+1 times as high as the speed used for recording and also for reproduction at a recording medium moving speed 4n+3 times as high as the recording speed while requiring virtually no change in the structural arrangement of the apparatus.
It is still another object of the invention to provide a video signal reproducing apparatus which permits reproduction under satisfactory tracking control at a recording medium moving speed 4n+3 times as high as the speed used for recording without requiring any change in the reference signal generating part used for conventional apparatus.